1. Field of the Invention
The present invention relates to a blade pitch controller, a wind turbine generator, and a method of controlling the blade pitch.
2. Description of Related Art
A wind turbine generator that generates power based on the rotation of a rotor to which a plurality of blades are turnably coupled is provided with, as described in JP2002-303255A, a hydraulic cylinder for driving the blades. Driving of the hydraulic cylinder allows each blade to turn with respect to the rotor, thereby changing a pitch of the blades.
Further, a variable displacement hydraulic pump (for example, an axial piston pump which is a swash plate hydraulic pump) is often used as a hydraulic pump that supplies hydraulic oil to the hydraulic cylinder. The hydraulic pump provides an advantageous effect that its discharge flow rate follows a load flow rate within a setting range of the pump.
However, while the discharge flow rate of the hydraulic pump follows the load flow rate, a discharge pressure of the hydraulic pump does not follow a load pressure. Accordingly, a differential pressure between the discharge pressure and the load pressure results in a dissipative energy, and lost mainly as a thermal energy, thereby increasing the temperature of the hydraulic oil.
Therefore, an output of an electric motor for driving the pump excessively increases by an amount of the differential pressure, and, in order to maintain the temperature of the hydraulic oil to be an adequate temperature, a cooling function such as an oil cooler is also required as the temperature increases due to the differential pressure.